500 WATT RADIOBEACON TRANSMITTER
ND2000A-02x-xx0
Page 2-16
15 January 2005
go high. This output will be passed to four separate
circuits.
One portion of U10B's output will be applied to the
base of transistor Q14. It will be forward biased and
turn on. Q14's collector (ground) will be passed to
connector J6-9 for external use. The output on U10B-
7 is also passed through inverter U6C to the cathode
of diode CR39. When U6C's output is low (SWR
present), diode CR39 will be forward biased and turn
on. A ground will be passed to SWR standby
connector J9-8 for internal use.
The control signal, representing a high SWR
condition, on the output of U10B-7 will also be
applied through buffer U4B and resistor R112 and
passed to the changeover circuits to inhibit the subject
transmitter from changing over when a high SWR
condition is present. A fourth portion of the high
SWR condition on the output U10B-7 will be applied
through resistor R111 and passed through
SWR alarm
connector J5-9 and applied to a
SWR-alarm
lamp on
the control/monitor's front panel. The
SWR-alarm
lamp will turn on when a high SWR condition is
present.
2.9.14
POWER TRIM INTERFACE
CONTROL CIRCUIT:
Operational amplifiers
U4C/D, U11A/B and their associated components
form the power trim interface control circuit for sides
A and B. Amplifiers U11A/B limit the output of
U4C/D to a level that will not exceed the intended RF
carrier output of either side (set by the respective
O/P
POWER
potentiometers on the mod drive PWBs). The
outputs of amplifiers U11A/B are applied through pwr
trim connectors J6-10/5.
2.9.15 REFLECTED
POWER/REFL
PWR
CAL CIRCUIT:
A DC voltage representing the
reflected power of the transmitter is passed through
refl pwr connector J8-4 and applied through load
resistors R90/91 to the inverting input of buffer
amplifier U9D. Capacitor C37 will charge through
resistor R92 to an average value representing the
reflected power. The output of U9D is applied
through resistor R104 and the
REFL PWR CAL
potentiometer and passed to refl pwr connector J5-2
for internal use. The
REFL PWR CAL
potentiometer
provides adjustment during calibration for the
reflected power indication being provided by
TEST
meter M1 on control/monitor panel A1. The reflected
power control signal from the output of U9D is also
applied through buffer U1D and passed to refl pwr
(remote) connector J8-1 for external use.
2.9.16 MOD% CONTROL CIRCUIT:
Operational amplifier U9A and its associated
components form a one-pole active low-pass filter/
attenuator. The input on J6-6, a DC voltage
proportional to the intended carrier level, is applied
through the filter/attenuator where the RF carrier
frequency will be removed but the audio information
will be passed.
One output of U9A is applied to U9B's non-inverting
input. A second output is applied through R27 and
the
SET 100% MOD
potentiometer to A7-8. A peak
detector, comprising CR4, R40 and C10, detects the
peak output on U9A. The detected signal is applied
through buffer U9C to J7-7. When the
TEST
switch is
set to
MOD-READ
, the meter will be placed between
the mod meter adjust line on J7-8 and the mod% on
J7-7. For 100% adjustment on the test meter,
TEST
switch on the control/monitor panel is set to mod-set,
the output on U9C will be double the output of U9A
to compensate for the return line through the meter
from the output of U9A.
2.9.17
AC POWER MONITOR CIRCUIT (DC
Option Installed):
The AC power monitor circuit
controls the status of the local and remote battery
alarm indications when the DC power source option is
installed.
When the AC power is satisfactory, a +15 VDC AC
sense input will be on J8-8/7. U6E output will be low
and control/monitor panel's
BATTERY-ALARM
lamp
will be off. The output of inverter/buffer U6D will be
maintained at a low (0.0 V dc) and transistor Q15 will
be reverse biased (turned off). An open collector will
be applied to J6-8 as the remote battery alarm output.
When the AC power fails, the AC sense input on
J8-8/7 will be 10K ohms to ground. U6E-12 will be
high and the control/monitor panel's
BATTERY-ALARM
lamp will turn on. The output of inverter/ buffer U6D
will be high (+15 V dc) and transistor Q15 will be
forward biased (turned on). A current sink to ground
will be applied to J6-8 as the remote battery alarm
output.
